I delivered a car to British Columbia two years ago and can
verify:
[1] There is a duty, tax, or whatever you want to call it,
imposed by Canadian customs. There's no lower limit on
this.
[2] There is no extra charge for air conditioning.
[3] The U.S. desires to impound cars for 72 hours [three
days] but the Canadians don't necessarily care. In our case
the Canadians rushed me through before the U.S. could come
over to sieze the car. It's merely a "gentleman's
agreement" that the U.S. imposes in order to deter
international car theft. You don't need to stop at U.S.
Customs to get into Canada.
--Roger van Hoy, '55DeSoto, '42DeSoto, '66Plymouth,
'73Duster, '81 Imperial, Washougal, WA